Adds _stylesheet to the resources to be generated.

[nickcharlton]

This produces a file like the following:

<%#
# Stylesheet Partial

This partial imports the necessary stylesheets on each page.
By default, it includes the application CSS,
but each page can define additional CSS sources
by providing a `content_for(:stylesheet)` block.
%>

<% Administrate::Engine.stylesheets.each do |css_path| %>
  <%= stylesheet_link_tag css_path %>
<% end %>

<%= yield :stylesheet %>

In app/views/admin/application/_stylesheet.html.erb. Fixes #888.

[sjnims]

@nickcharlton not sure if this is intentional, but are you rendering the stylesheet outside of turbolinks on purpose?

[nickcharlton]

@professorNim There's no direct dependency on turbolinks, as we've tried to keep the dependencies small.

[MyklClason]

Not related to this, but I wanted to override the layout and found that using layout :application and adding:

<% Administrate::Engine.stylesheets.each do |css_path| %>
  <%= stylesheet_link_tag css_path %>
<% end %>

to the layouts/application.html.erb (before the application layouts are loaded so they can be overrode) to work like a charm. As changing the layout messes up the style sheets. So kudos for this.